Electrode layout for blood test sensor strip

ABSTRACT

An improved electrode layout for a continuous strip sensor is provided which reduces misalignment of the electrodes with the contacts which read the position of the strip. Better contact with the electrodes reduces or eliminates transient signals between stop positions of the sensor strip.

This application is a divisional of U.S. application Ser. No.12/689,654, filed on Jan. 19, 2010, now U.S. Pat. No. 8,771,202.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is in the field of blood sample acquisition and testing.In particular, the invention is directed to a sensor strip used in adevice that performs both a lancing operation to acquire a blood sampleand a measurement operation on the sample in one user-initiated step.The strip is provided with a plurality of test sites, and may be woundon a supply wheel and fed through the device between the supply wheeland a take-up wheel, so that a single strip may be used to obtain aplurality of measurements.

2. Description of the Related Art

Self-monitoring of blood glucose generally requires the user to extracta volume of capillary blood and place it on a disposable element foranalysis. Devices for lancing a subject at an extraction site to obtaina small quantity of blood for testing on a test strip are known in theprior art. For example, U.S. Pat. No. 6,558,402, which is incorporatedby reference, discloses a lancer having suitable mechanisms for piercinga subject's skin and obtaining a sample.

Test strip sensing elements using amperometric and other techniques fordetermining the concentration of blood glucose in a blood sample areknown in the prior art. U.S. Pat. Nos. 6,143,164, and 5,437,999,incorporated by reference herein, each disclose examples of test stripconstruction for electrochemical measurement of blood glucose.

The integration of lancing and sensing would be a desirable advance inthe self-monitoring of blood glucose. U.S. patent application Ser. No.12/502,594, filed Jul. 9, 2009, describes such a “two-in-one” device,wherein a single test strip contains a plurality of test sites, whichcan be advanced automatically through a testing device. In this context,it would be desirable to have a layout of electrodes and contact pads ona test strip to permit automatic advancement of the strip through thedevice, that would account for variations in alignment, and to eliminatetransient signals as the strip is indexed through different stop pointsin the lancing/sensing process and on to the next test position on thestrip.

SUMMARY OF THE INVENTION

According to the present invention, an elongated sensor strip for use ina blood sample test device is provided comprising a plurality of testsites arranged in series in a travel direction on the strip. Each testsite includes a lancet hole, electrodes for determining a blood samplevolume, and test electrodes for determining a blood samplecharacteristic. Each test site on the strip comprises a non-conductivesubstrate layer and a conductive layer, which is formed into electrodesand conductive pads (such as by etching non-conductive lines in theconductive layer). The conductive pads are aligned with device contactsin the blood sample test device. A non-conductive layer is superposed onthe conductive layer and has a window exposing a plurality of theconductive pads.

The conductive pads of the sensor strip are preferably formed bydepositing a conductive layer and etching lines to form conductive padsin columns aligned with device contacts in a blood test device. Rows ofthe conductive pads correspond to stop positions in the lancing/sensingoperation during which a blood sample is accumulated on the strip andthen moved to a position where a blood glucose measurement is taken.Horizontal traces in the sensor strip which connect the electrodes onthe strip with the conductive pads (which are perpendicular to thetravel direction of the strip) are covered by a non-conductive coverlayer, so that the horizontal traces are not directly contacted by thedevice contacts as the strip advances through the device.

A blood sample acquisition and sensing system according to the inventioncomprises a housing containing device contacts and the elongated striphaving a plurality of test sites arranged in series in a traveldirection on the strip, as described above. Each test site includes alancet hole, electrodes for determining a blood sample volume, testelectrodes for determining a blood sample characteristic, and conductivepads aligned in columns with the contacts on the blood test device formaking electrical contact between the strip and the device contacts. Thesystem also comprises a lancet and lancet injector, a motor foradvancing the strip, and a processor. The processor is adapted toprocess signals produced when the device contacts make electricalcontact with the conductive pads on the strip at stop positions in thelancing/sensing process, and to communicate with the lancet injector,the test electrodes, and the motor. In a preferred embodiment, theelements of the system, including the strip, lancet and lancet injector,motor and processor are provided in a unitary housing which may beprovided with user-operable controls and a display.

A method for performing a plurality of blood sample acquisition andtesting procedures on a strip according to the invention comprises thesteps of: providing an elongated strip, such as described above, havinga plurality of test sites arranged in series in a travel direction onthe strip, wherein each test site includes a lancet hole, electrodes fordetermining a blood sample volume, test electrodes for determining ablood sample characteristic, and conductive pads for making electricalcontact with a blood test sensor device; injecting a lancet through thelancet hole at a first test site into a subject to obtain a blood samplecontacting the strip; contacting the blood sample with the electrodesfor determining a blood sample volume so that a signal is produced whena blood sample volume is detected; advancing the strip responsive to thesignal produced when a blood sample is detected; contacting the bloodsample with the test electrodes to obtain a blood sample characteristicsignal; and advancing the strip to a second test site.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a test site on an elongated sensor strip according to anembodiment of the invention.

FIG. 2 depicts a matrix of showing the state of the electrodes at eachstop position of the strip during the lancing/sensing process in anembodiment of the invention.

FIG. 3 depicts an embodiment of the system according to the invention,in which the sensor strip, lancet and processor are enclosed within aunitary housing.

FIGS. 4A, 4B, 4C and 4D depict layers of the test strip, forming anexploded view of the structural features in a test site.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 schematically depicts a portion of an elongated sensor strip 20according to an embodiment of the invention, including the elementsfound in a test site. A plurality of such test sites are provided inseries along the travel direction 12 of the strip. Thus, each test siteincludes a lancet hole 30, electrodes 41, 42 for determining a bloodsample volume, and test electrodes 43, 44 for determining a blood samplecharacteristic, all of which are arranged on a non-conductive substratelayer 50.

The material of the non-conductive substrate layer is not particularlylimited and may be, for example, polyethylene terephthalate (PET) havinga thickness in a range of about 5 mils to about 15 mils. The electrodesare preferably formed by sputtering a metal, such as gold, to form aconductive layer having a thickness in a range of about 50 Angstroms toabout 2000 Angstroms, and etching a pattern to form the electrodes andconductive pads. Conductive pads, such as pad 45, are preferably formedfrom the same conductive layer by etching non-conductive lines, such asline 35. Other conductive materials and/or methods of depositing and/orpatterning may be used. A non-conductive cover layer 90 forms a window,depicted by dotted line 52, exposing the pads to the contacts in thedevice as the strip is indexed through the device.

In a preferred embodiment, the horizontal traces, such as trace 47between conductive pad 45 and electrode 42 are protected by thenon-conductive cover layer 90 so that they are not severed by the devicecontact, and to minimize noise signals.

In a preferred embodiment, the leading edge of a first conductive pad,which is defined by a non-conductive line, is in front of a leading edgeof another pad in the same row. In this way, the order in which signalsare collected from the pads can be controlled. Thus, in each of rows 22,23 and 24 (lance, detect, and acquire positions respectively); onecontact has a shifted leading edge. For example, the leading edge ofconductive pad 33 is behind the other pads in row 24 in respect of thetravel direction, and is connected to the common ground. The leadingedge of conductive pad 53 is behind pad 45 in row 23 and is connected tothe common ground. Conductive pad 73 is behind the pressure switch padPS in “lance” row 22. Pads 33, 53 and 73 are connected to a conductor atcolumn 28, which is contacted by a grounding contact in the device toprovide a reference. Column 28 is always grounded in the lance, detect,and acquire states represented by rows 22, 23 and 24. All of theconductive pads preferably have a surface area in a range of about 1.0mm² to about 3.0 mm².

The structural layers of the test strip form features typical of anindividual test strip, including a capillary channel and reagent wells.U.S. application Ser. Nos. 12/502,594 and 12/502,585, both filed Jul. 9,2009 by the Assignee herein, and incorporated by reference herein,describe these details of the strip structure.

Referring to FIG. 4A through 4D, FIG. 4D shows non-conductive substratelayer 50 with a conductive pattern 69 of pads and traces formed thereon.FIG. 4C shows a non-conductive structural layer with the features of thereagent wells 92, 94 aligned with corresponding electrodes. FIG. 4Bdepicts a spacer layer which forms a capillary channel between thelancet hole and the wells. Top layer 4A forms vent 96. The top layer,spacer layer and structural layer share a window 52, which exposesconductive pads, but protects horizontal traces.

The conductive pads are arranged into columns 25, 26, 27, and 28, whichare aligned with contacts in the device (not shown), which press againstthe sensor strip as it advances through the device. Rows of pads 21, 22,23, and 24 correspond to positions of the tape in the lancing/sensingprocess. Lancet hole 30 is provided so that a lancet in the device canbe injected through the hole into a subject's body. Sprocket hole 32 isprovided in the strip so that a motor can control the advancement of thestrip through the device in precise increments using a sprocketmechanism.

In the course of using the sensor strip, a lancet is injected throughlancet hole 30 to obtain a blood sample. The blood sample is collectedin the space between electrodes 41 and 42, which are connected by tracesto conductive pads 49 and 45, respectively. When sufficient blood sampleis accumulated, an electrical short is detected between electrodes 41and 42, and a processor signals the motor to advance the strip indirection 12. Moving the strip causes the blood sample to be conductedto the test electrodes 43 and 44 at the bottom of corresponding reagentwells. Data from the electrochemical measurement of the blood glucosecontent of the sample is collected from signals generated by electricalcontact made between device contacts and associated conductive pads 34and 37. This information is routed to the processor for display, on thedevice housing or otherwise, and the sensor tape is thereafter advancedto the next test site on the strip so that the lancing/sensing processcan be repeated.

FIG. 2 depicts a matrix which describes the state of the conductive padsat stop positions in the lancing/sensing process. The matrix comprisesrows 10, 14, 16, and 18, and columns 11, 21, 31, and 41 corresponding tothe conductive pads in an exemplary embodiment of the invention.

FIG. 2 depicts three active states and a home position. At the homeposition, depicted as row 10, first, third and fourth conductive padsare grounded and the second conductive pad is unused because it is notneeded. This is the state of the device prior to conducting a lanceoperation. The device is not used in the home state. When the system isactivated, the strip is positioned so that pressure sensor PS on thestrip can be pressed against a subject's skin. This is the lanceposition of the strip, depicted as row 14, so that when the strip is inthis position, the third and fourth contacts are grounded and the secondcontact is unused. At the lance position, the second contact is unuseddue to the presence of the lancet hole 30. At the detect position, inwhich a blood sample volume is detected, the second contact is grounded,the first contact is connected to the Top Detect Switch and the thirdcontact is connected to the Bottom Detect Switch, represented in row 16(i.e., the electrodes for determining a blood sample volume). When ablood sample creates an electrical short between electrodes 41 and 42the switches in row 16 give the signal to the processor. At the acquireposition, represented by row 18, the first contact is grounded, thesecond contact is connected to the “Rear Capillary Switch” and the thirdcontact is connected to the “Front Capillary Switch,” (i.e., theelectrodes for determining a blood sample characteristic). The groundedcontact is routed to the common ground in column 28, to minimize falsereadings. The signal for glucose reading produced by electrodes 43, 44is sent to the processor through switches in row 18. Preferably, atleast one of the test electrodes is active so that a current can bepassed through the sample to obtain a blood glucose measurement.

The advancement of the strip is driven by a motor in response tocommands from a processor. A control system stops the motor when aselected contact encounters the edge of a grounded electrode. The sensorstrip may be wound on a supply wheel and taken up by a take-up wheel asthe strip advances through the device. Sprocket holes 32 in the stripensure that the motor advances the strip in controlled increments.

As shown in an embodiment depicted in FIG. 3, a blood sample acquisitionand sensing system may combine the elements described above in a unitaryhousing 60. Thus, an elongated sensor strip 84, having the featuresdescribed above, may be provided to the housing on a supply wheel 54,and as the strip is advanced through the device, the sensor strip may betaken up on take-up wheel 56. Processor 82 communicates with a motor(not shown) to advance the strip, preferably using sprocket on thestrip, so that the incremental advancement of the sensor strip isaccurately controlled and not affected by the variation in the thicknessof the layers of sensor strip being wound around the take-up wheel 56.The processor may communicate with user operable controls 64, 66, and adisplay 62 so that a user can conveniently control the system forself-monitoring of blood glucose. The elements are powered by anysuitable power supply 80, such as a battery. The processor 82communicates with lancet injector 74 to inject lancet 72 through thelancet hole on the strip.

The above description of the preferred embodiments should not be deemedas limiting the invention, which is defined by the following claims.Features described in the dependent claims are further aspects of thepreferred embodiments, which may be used in combination.

What is claimed is:
 1. A method for performing a plurality of bloodsample acquisition and testing procedures on a strip having a pluralityof test sites arranged in series in a travel direction on the strip,wherein each test site includes a lancet hole, first electrodes forproducing a first signal when a sufficient volume of a blood sample isdetected, second electrodes for obtaining a second signal characteristicof the blood sample, and a plurality of conductive pads that are alignedin a matrix of rows and columns and are aligned to make electricalcontact with device contacts on a blood test sensor device, wherein theconductive pads for the first electrodes are electrically connectedthereto by respective conductive traces, wherein the conductive pads forthe second electrodes are electrically thereto by respective conductivetraces, and wherein a leading edge in the travel direction of a firstconductive pad in a row is in front of a leading edge in the traveldirection of a second conductive pad in the same row, comprising thesteps of: injecting a lancet through the lancet hole at a first testsite into a subject to obtain the blood sample; contacting the bloodsample with the first electrodes; advancing the strip in response to thefirst signal produced by the first electrodes; contacting the bloodsample with the second electrodes to obtain the second signal; andadvancing the strip to a second test site.
 2. The method according toclaim 1, wherein: at least three separate rows of conductive padscorrespond to at least a lancing step position, a blood volume detectionstep position, and a blood characteristic sensing step position of thestrip in a lancing/sensing process; at least four columns of conductivepads are aligned with respective device contacts; and at least two ofthe conductive pads in each said row are grounded at each of saidpositions in the lancing/sensing process.
 3. The method according toclaim 2, further comprising the step of producing a signal correspondingto a home position when electrical contact is made with conductive padsin a fourth row.
 4. The method according to claim 1, further comprisingthe step of detecting the pressure of the strip against the subjectprior to injecting the lancet into the subject.
 5. The method accordingto claim 1, further comprising the step of obtaining the first signalwhen a blood droplet bridges a pair of first electrodes causing them toshort.
 6. The method according to claim 1, further comprising the stepof passing current through the blood sample to obtain the second signal.7. The method according to claim 1, wherein a non-conductive cover layeris provided over the conductive traces.
 8. The method according to claim6, wherein the second signal corresponds to an electrochemicalmeasurement of blood glucose.
 9. The method according to claim 7,wherein the non-conductive cover layer has a window to expose theconductive pads to the device contacts.